The concentration of U, 226Ra, Th, and222 Rn in ground and underground water samples were determined during 1992–1994 as part of an extended program of ecological study of the Danube Delta and its limitrophe area. The analytical methods are briefly presented along with the results obtained for 23 sampling sites. The amounts in the surface waters are below the maximum permissible concentrations for drinking water. Relatively higher thorium and radon contents were observed in the underground water samples.
